1. Field of the Invention
The present invention relates to a data storage apparatus, such as a disk drive apparatus, and a method for fixing disks to drive means.
2. Description of the Related Art
Recently, there have been increasing demands for the miniaturization and augmentation of capacity of magnetic disk apparatuses, such as hard disk drives (hereinafter referred to as HDDs). As a measure to increase the capacity of compact HDDs which use 2.5-inch disks or smaller ones, in particular, there is an effective method in which the recording density is improved by reducing the flying height of a magnetic head with respect to a magnetic disk.
Reducing the size and increasing the capacity of the HDDs by this method, however, involve a special problem, deformation of the disk caused as the disk is fixed to a spindle motor. If the disk is a deformed one, the gap between the magnetic head and the disk, that is, the flying height of the head above the disk, varies. The smaller the flying height, the larger this variation will be. The variation of the flying height results in an output fluctuation, which lowers the reliability of recording and reproducing operations.
A method of fixing magnetic disks is disclosed in FIG. 1 of U.S. Pat. No. 4,945,432. Specifically, in fixing disks, e.g., two in number, to the spindle motor, in any of the conventional HDDs, these disks are put in layers on a flange portion at one end of a hub of the motor with use of a spacer between them, and are fixed to the hub by means of a disk retainer at the other end of the hub. In doing this, the disk retainer is fixed to the hub by means of a plurality of screws. According to this method, however, the force acting on each disk is not uniform with respect to the circumferential direction, so that the disk is deformed in a manner such that it has as many indentations as the screws in the circumferential direction.
Also known is a method in which the disk retainer is fixed to the hub by means of one screw. According to this method, a uniform force acts on each disk with respect to the circumferential direction, so that the circumferential deformation of the disk is reduced. Since the disk is subject to a radial deformation, as well as the circumferential deformation, however, it is deformed in the shape of a bowl as a whole.
Even with the magnetic disk depressed in this manner, the magnetic head flies above the disk surface which is deformed in the longitudinal direction of the head. Thus, the flying height of that portion of the magnetic head, which corresponds to the magnetic gap, above the disk is different from the flying height in the case wherein the disk surface is flat, thereby influencing output signals. This arouses a serious problem in the use of the compact HDDs for 2.5-inch or smaller disks, in particular.